A senior police officer has said the UK will lose access to a major database of criminal information, whether or not it secures a Brexit deal with the EU.
Steve Rodhouse, director general of operations for the National Crime Agency, said the UK could no longer use the ‘SIS2’ database.
UK and EU talks are ongoing ahead of the 31 December deadline for a deal.
Foreign Secretary Dominic Raab has previously told the BBC’s Andrew Marr security will improve after Brexit.
Mr Raab also said the UK was seeking access to some of the tools used in the EU as part of “common sense co-operation”.
The UK left the EU on 31 January, but continues to follow current EU rules until the end of the year while negotiations take place.
Any deal would need to be ratified by parliaments on both sides.
On security, the UK had wanted to maintain the same access to shared databases that it has now, but the EU says that is not on offer to non-members.
Mr Rodhouse warned that around 40,000 alerts relating to investigations in other European countries would disappear from the UK’s police national computer on 31 December.
He said: “Investigations could take longer, and it could mean that serious criminals are not held to account as quickly.”
EU member states use the Schengen Information System (SIS) database, which sends out alerts to police and border guards.
UK police will switch to the Interpol “red notice” system for international investigations in Europe, but Mr Rodhouse told the Home Affairs committee he was unsure whether EU countries would use it.
“It is right for me to raise the prospect that there will be some EU member states in some circumstances who don’t use Interpol alerts and of course if the UK doesn’t have access to SIS 2 that provides a gap for us,” he said.
“I’m led to believe that many of the capabilities or tools can be replicated but certainly not all.”
Deputy Assistant Commissioner Richard Martin from the National Police Chiefs Council said that around 9,000 pieces of information from the EU database had been moved to the Interpol system.
Mr Rodhouse said he had been in close touch with the Home Office during the negotiations but was “not sighted” on the detail of any possible agreement.
In October, cabinet minister Michael Gove said “there are many, many areas in which we can co-operate more effectively to safeguard our borders outside the European Union”.